// InflaterHuffmanTree.cs
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;
using ICSharpCode.SharpZipLib.Zip.Compression.Streams;

namespace ICSharpCode.SharpZipLib.Zip.Compression 
{
    
    /// <summary>
    /// Huffman tree used for inflation
    /// </summary>
    public class InflaterHuffmanTree
    {
        #region Constants
        const int MAX_BITLEN = 15;
        #endregion

        #region Instance Fields
        short[] tree;
        #endregion

        /// <summary>
        /// Literal length tree
        /// </summary>
        public static InflaterHuffmanTree defLitLenTree;
        
        /// <summary>
        /// Distance tree
        /// </summary>
        public static InflaterHuffmanTree defDistTree;
        
        static InflaterHuffmanTree()
        {
            try {
                byte[] codeLengths = new byte[288];
                int i = 0;
                while (i < 144) {
                    codeLengths[i++] = 8;
                }
                while (i < 256) {
                    codeLengths[i++] = 9;
                }
                while (i < 280) {
                    codeLengths[i++] = 7;
                }
                while (i < 288) {
                    codeLengths[i++] = 8;
                }
                defLitLenTree = new InflaterHuffmanTree(codeLengths);
                
                codeLengths = new byte[32];
                i = 0;
                while (i < 32) {
                    codeLengths[i++] = 5;
                }
                defDistTree = new InflaterHuffmanTree(codeLengths);
            } catch (Exception) {
                throw new SharpZipBaseException("InflaterHuffmanTree: static tree length illegal");
            }
        }

        #region Constructors
        /// <summary>
        /// Constructs a Huffman tree from the array of code lengths.
        /// </summary>
        /// <param name = "codeLengths">
        /// the array of code lengths
        /// </param>
        public InflaterHuffmanTree(byte[] codeLengths)
        {
            BuildTree(codeLengths);
        }
        #endregion

        void BuildTree(byte[] codeLengths)
        {
            int[] blCount  = new int[MAX_BITLEN + 1];
            int[] nextCode = new int[MAX_BITLEN + 1];
            
            for (int i = 0; i < codeLengths.Length; i++) {
                int bits = codeLengths[i];
                if (bits > 0) {
                    blCount[bits]++;
                }
            }
            
            int code = 0;
            int treeSize = 512;
            for (int bits = 1; bits <= MAX_BITLEN; bits++) {
                nextCode[bits] = code;
                code += blCount[bits] << (16 - bits);
                if (bits >= 10) {
                    /* We need an extra table for bit lengths >= 10. */
                    int start = nextCode[bits] & 0x1ff80;
                    int end   = code & 0x1ff80;
                    treeSize += (end - start) >> (16 - bits);
                }
            }
            
/* -jr comment this out! doesnt work for dynamic trees and pkzip 2.04g
            if (code != 65536) 
            {
                throw new SharpZipBaseException("Code lengths don't add up properly.");
            }
*/
            /* Now create and fill the extra tables from longest to shortest
            * bit len.  This way the sub trees will be aligned.
            */
            tree = new short[treeSize];
            int treePtr = 512;
            for (int bits = MAX_BITLEN; bits >= 10; bits--) {
                int end   = code & 0x1ff80;
                code -= blCount[bits] << (16 - bits);
                int start = code & 0x1ff80;
                for (int i = start; i < end; i += 1 << 7) {
                    tree[DeflaterHuffman.BitReverse(i)] = (short) ((-treePtr << 4) | bits);
                    treePtr += 1 << (bits-9);
                }
            }
            
            for (int i = 0; i < codeLengths.Length; i++) {
                int bits = codeLengths[i];
                if (bits == 0) {
                    continue;
                }
                code = nextCode[bits];
                int revcode = DeflaterHuffman.BitReverse(code);
                if (bits <= 9) {
                    do {
                        tree[revcode] = (short) ((i << 4) | bits);
                        revcode += 1 << bits;
                    } while (revcode < 512);
                } else {
                    int subTree = tree[revcode & 511];
                    int treeLen = 1 << (subTree & 15);
                    subTree = -(subTree >> 4);
                    do {
                        tree[subTree | (revcode >> 9)] = (short) ((i << 4) | bits);
                        revcode += 1 << bits;
                    } while (revcode < treeLen);
                }
                nextCode[bits] = code + (1 << (16 - bits));
            }
            
        }
        
        /// <summary>
        /// Reads the next symbol from input.  The symbol is encoded using the
        /// huffman tree.
        /// </summary>
        /// <param name="input">
        /// input the input source.
        /// </param>
        /// <returns>
        /// the next symbol, or -1 if not enough input is available.
        /// </returns>
        public int GetSymbol(StreamManipulator input)
        {
            int lookahead, symbol;
            if ((lookahead = input.PeekBits(9)) >= 0) {
                if ((symbol = tree[lookahead]) >= 0) {
                    input.DropBits(symbol & 15);
                    return symbol >> 4;
                }
                int subtree = -(symbol >> 4);
                int bitlen = symbol & 15;
                if ((lookahead = input.PeekBits(bitlen)) >= 0) {
                    symbol = tree[subtree | (lookahead >> 9)];
                    input.DropBits(symbol & 15);
                    return symbol >> 4;
                }

                int bits = input.AvailableBits;
                lookahead = input.PeekBits(bits);
                symbol = tree[subtree | (lookahead >> 9)];
                if ((symbol & 15) <= bits) {
                    input.DropBits(symbol & 15);
                    return symbol >> 4;
                }

                return -1;
            }

            {
                int bits = input.AvailableBits;
                lookahead = input.PeekBits(bits);
                symbol = tree[lookahead];
                if (symbol >= 0 && (symbol & 15) <= bits) {
                    input.DropBits(symbol & 15);
                    return symbol >> 4;
                }

                return -1;
            }
        }
    }
}

